The following description will refer particularly to large, natural draft cooling towers of hyperbolic shape, such as are commonly used in power stations. However, the invention is also applicable to other types of cooling tower, such as forced or induced draft cooling towers.
In a cooling tower, process water is passed downwardly against a counter-flow of cooling air. The water is typically distributed by pipes across the top surface of a packing or fill pack. The fill pack is present to break up the water into droplets so as to produce a large surface area of water for contact with the cooling air, and the fill pack typically consists of plastic tubes and flutes.
Over time, fouling builds up in the fill pack. The fouling consists of scale from minerals and organic matter precipitated from the process water, and biological fouling consisting for example of algae and bacteria. The fouling reduces the available flow area and thus efficiency, and is also a potential health hazard. Periodic cleaning of the fill pack is therefore necessary.
Traditionally, due to difficulties in accessing, removing and cleaning the fill pack, towers have often become exponentially fouled. Techniques for combatting this have focused on on-going water treatment/dosing and/or filtration; these can act to slow down fouling but essentially only limit the rate of build-up. Traditional methods of cleaning have involved pack removal and high pressure jetting; this has problems such as damage to the fill pack during removal, erection of containment areas to limit bacterial spread, and issues of time and cost.
Experience has shown that cooling tower users desire an ability to gauge the level of fouling over time. This information can allow better interim management and decision making as to maintenance options. Hitherto this has been attempted by removal of pack sections for visual inspection, and removal and in-situ pack weighing. More recently, endoscopic techniques have been used to visually check pack flutes for deposition. These all have some utility but each has drawbacks, notably that they all check isolated sections to act as representative for the entire tower.
The present invention seeks to overcome or mitigate these problems.